This parable was prompted by the request of one of two brothers. "And one of the company said unto him, Master, speak to my brother, that he divide the inheritance with me," Luke 12:13. One wanted MORE of the inheritance while the other wanted to hold onto MORE of the inheritance than was just!
Covetousness is an improper desire for the property of another. It is also a desire of gain or riches beyond what is necessary for our needs. It is a breach of the 10th Commandment. "Thou shalt not covet thy neighbour's house, thou shalt not covet thy neighbour's wife, nor his manservant, nor his maidservant, nor his ox, nor his ass, nor any thing that is thy neighbour's," Exodus 20:17.
It is in bad company!! It is expressly called idolatry in Col 3:5.
"Mortify therefore your members which are upon the earth; fornication, uncleanness, inordinate affection, evil concupiscence, and covetousness, which is idolatry."
It is also mentioned in other places. "But fornication, and all uncleanness, or covetousness, let it not be once named among you, as becometh saints," Ephesians 5:3.
"Let your conversation be without covetousness; and be content with such things as ye have: for he hath said, I will never leave thee, nor forsake thee," Hebrews 13:5. Having the Lord we have all things!!
So the Lord is dealing with a very serious sin which is common amongst all men of all ages and nations.